A wide variety of applications exist in commerce and industry wherein materials and products that are susceptible to corrosion may be protected from corrosive environments through the use of packaging or wrapping films. A common example of items in need of protection from corrosion involve materials and/or products manufactured from corrosion-susceptible metals, which tend to corrode through oxidation when exposed to oxygen in either a gaseous or liquid phase. As such, elements in the atmosphere such as gaseous oxygen and water vapor are agents that tend to cause corrosion in metal materials.
Various film forms have been developed and implemented as wrapping about such corrosion-susceptible materials. Examples of such films are discussed in U.S. Pat. Nos. 5,855,975, 6,156,929, 6,420,470, and 7,588,820, the contents of which are incorporated by reference herein. Further examples of films are discussed in European Patent Application Publication No. 1,916,276. Films for wrapping about corrosion-susceptible materials are often referred to as packaging films, as they are often times utilized in conjunction with product packaging applications. However, such films may also or instead be utilized in protective wrapping applications not commonly associated with product packaging. While films fabricated solely of polymeric materials assist in preventing corrosion agent access to the enclosed materials, certain films having further corrosion inhibiting characteristics have been developed and implemented.
Films currently utilized in corrosion inhibiting applications include those which contain vapor corrosion inhibitor (VCI) materials which vaporize from the film into the enclosed package to minimize corrosion caused by aggressive species entering into or contained within the enclosure. A commonly used VCI ingredient comprises nitrite salts, especially sodium nitrite. While nitrite salts are effective, cost competitive, and generally safe to use, they have come under increased scrutiny recently due to environmental and safety concerns. These concerns have prompted a desire for effective VCI films without any nitrite salts in the product.
VCI materials are commonly incorporated in thermoplastic (e.g. polyethylene) via a melt blending process. Corrosion inhibiting thermoplastic alloys are discussed in U.S. Pat. No. 6,555,600, the contents of which are incorporated by reference herein. The VCI materials are preferably present as a particulate material, which becomes dispersed in the thermoplastic. The particle size needs to be sufficiently small so as not to interfere with processing or film forming. The VCI materials also need to be reasonably thermostable at the melt processing temperatures, which are typically in the range of 150-250° C. for polyethylene. Some VCI materials are prone to degradation or chemical reactions at these temperatures. VCI materials with high vapor pressure at these temperatures may show excessive loss due to vaporization. VCI materials that melt at these temperatures may create processing problems due to phase separation and pooling in the extruders. Nitrite salts have been shown to be very stable and effective in melt processing of thermoplastic films. Many potential alternatives are not suitable due to one or more of the above problems.
It is the object of the present invention to provide a packaging film containing a nitrite free combination of VCI materials as a corrosion inhibiting agent.
It is a further object of the present invention to provide a multilayer packaging film in which only some of the layers contain a nitrite free combination of VCI materials as a corrosion inhibiting agent.